Grips-remind me again...

http://golfpride.com/FAQs.aspx#in_between_size

This link says 1 wrap of tape = 1/64". If you are using 4 wraps, that means you are +1/16. The chart shows installing a .580 grip (58) on a .620 shaft only gives you +1/32. Looks like you will need 2 wraps, even with the .580 grips.

No, I believe you're doing it backwards. The smaller core "grows" the overall diameter of the grip when put on a larger diamter shaft. A .580 on a .580 is, let's say "0.00". If you put that .580 on a .610 shaft, you expand the outside by .030... making it a larger feeling grip. If you get .600 grips and install them on .610 shafts, you are only expanding the outside diamter .010 and they won't feel as large.
In your case, you currently have the .580 grips on .610 shafts plus 4 wraps of tape. Each tape wrap is 1/64", or .015. Using 4 wraps, you are actually only adding 3 wraps to the formula, since every grip is sized to accomdate a single wrap of tape. So, the grips alone enlarge the OD of the grip by .030, plus .045 for the tape. You are now playing grips that are .075 oversize. If you use .600 grips and only gain .010 you would need .075 less .010 or .065. With each wrap of tape equaling .015, you would need a little over 4 EXTRA wraps or 5 wraps total to get to the same size you now have. Whew!!! Have I lost you yet?
You seem to like the +.075 grips. Why don't you just purchase larger grips?? Midsize GPs or Lamkins have .600 cores. The Midsize are +1/16" and the Oversize are +1/8". Converting to decimals, the Midsize are +.062. You will already be expanding the .600 core grip .010 installing it on a .610 shaft. That that makes the midsize... with only the standard single tape wrap... +.072.... Exactly where you are now at .075. Now, I'm really out of breath.
FYI, I use Lamkin Crossline Midsize on everything, including my JZ shafts in the BeCu Pings. After all this figuring, I have basically the same thing you are looking for. I have attempted to go back to standard grips and they just don't feel right. Love the Midsize!!! You can order them online from Golfsmith or GolfWorks. We had a Dick's open in our town about a year ago and they have the Midsize Crosslines for $3 +/- grip.

I'm more anal about the potential of multi-layers of tape "shifting" than I am slight deviations in overall diameter. I want the grip as close to the shaft as possible, without any additional wraps that could allow movement. But, that's just me.
Another thing you might try is to special order one "yellow" Ping grip. The "yellow" lettered Pings are supposed to be midsize. However, I've always thought they felt a tad bit smaller than the Lamking/GP midsize grips. Again, Golfsmith or GolfWorks usually have the OEM Ping grips available.
(Your I3's would look so much better with "real" Ping grips!!!)

I play without a glove, so I only use wrap-style grips.

The Winn Dri-Tac Wrap has replaced the standard Golf Pride Tour Wrap in my bag, but the jury is out as to its durability. So far, so good.

I love real leather grips, but these days, they're expensive, and every pro shop doesn't have them.

Put your grips on with compressed air. NO tap. Super solid and reliable. Playable immediately. CAN'T BELIEVE I EVER DID IT ANY OTHER WAY. Seriously. And you can take grips off, put other ones on, switch them back, etc. No contest.

Do you still use tape? Do you just use a basketball needle?

http://www.golfworks.com/product.asp_Q_pn_E_GW0103_A_cn_E_17

I've got some sort of copper tube thing attached to an air compressor. NO tape whatsoever. A little soapy water on the end of the grip to work it over the end of the shaft. Once I work it on a half-inch, I slowly increase the air pressure until it creates this little cushion and I can push it all the way on. Literally ready to play IMMEDIATELY. Turn the air off, pull the copper out, good to go. Done. SO easy to adjust and remove/reapply the grip if need be.

A WORD OF WARNING... when removing a grip, you need a piece of PVC pipe or something to put over the grip. IF you just blow air into the back, the grip WILL BLOW UP to the size of a huge sub sandwich. It's terrifying if you're not ready for it. The PVC pipe only allows the grip to expand a little, then the "seal" between the grip and the club is broken and you can slide the grip right off.

This is especially important when you're "blowing off" grips that were applied with tape. You need a lot of pressure to break the seal between the mouth of the grip and the club/tape. Without PVC pipe to restrict the expansion of the grip, you're going to be freaked out by just how much you can blow these things up. It actually scared me off of using air until I talked to eClark via TigerWoods'12 on xbox 360 about it and he turned me on to the PVC pipe.

Thanks SUX