Bicycle Mechanics - Chain wrap/cassette Shimano RD 6401 question

I'm swapping components on an old Panasonic DX-4000 7 speed to some 8 speed stuff.(sport exage lx to 600tricolor). I have a Shimano RD-6401 (short cage) and FD-6401 with ST-6400 8 speed brifters and am wondering what cassette to use. I have two choices for chainrings, either a 52/39 or 52/42. I'm thinking of a new Mavic open pro/ultegra wheelset, but not sure on that yet. The VeloBase website says the RD has a max of 28t for cog and also 28 for chainwrap, any thoughts on what to use? Does a 12-26 with the 52/39? 11-28 with the 52/42? something else??

You won't need an 11 cog with either a 53 or a 52 big ring.
The cassette that will work with you best depends primarily on where you plan to ride, the terrain and wind conditions. Your strength is also important.
I have 20 years of experience on road bikes. I ride various conditions, hills and wind. not mountains. All of my cassettes start with a 13. Mostly I ride with 53/39 chainrings and a 13-26 cassette. Sometimes I wish I had a lower gear. You really don't need a 12 cog unless you are spinning out the 52-12 combination at 120 rpm, or so, cadence on level ground. A 52-12 at 100 rpm is good for at least 34 mph. If you are traveling faster than that down a steep hill you can gain more speed by getting your body in a good aerodynamic tuck.
The 52/39 combined with a 12-26 needs a 27 tooth wrap capacity derailleur to be on the safe side. So you're good. (52-39) + (26-12) = 27

Thanks.