I'm in the process of upgrading my old centurion ironman from the old 6 speed 105 system to a modern 10 speed. I was given some wheels for free with a 10 speed tiagra cassette (12-13-14-15-17-19-21-24-27-30), and I picked up some 10 speed dura ace downtube shifters, and an ultegra 6600 rear derailer. I have the old 105 derailer on the front. I picked up a kmc 10 speed chain on ebay, but neglected to check beforehand to make sure that it would be long enough. Sure enough, with my old 52t biopace outer ring, the chain is about two links short (i.e. using the Sheldon method of setting the chain on the big sprocket and the big ring, without threading through the derailer, I could just barely join the ends, using the powerlink.

But I also noticed that the links in the chain are not quite matching up right with the teeth on the old biopace chainring, which seems to indicate that the chainring is worn and needs to be replaced. I've also been thinking lately that I don't need a 52-42 on the front, anyway. Most of the time, I would end up on the smaller ring, but on the higher end of the cassette, so I would end up using only 2-3 gears, and almost never use the higher gears on the big ring. Seems like a waste. I think it just makes more sense to bring down my chainrings; 46 on the outside would be ideal (but maybe 48, if availability is tough), with 38 or 39 on the inner ring. I have the old 105 cranks on there (130 bcd, I assume).

So here are my questions:
If I go down from 52 to 46 on the outer ring, will that give me enough clearance to use the current chain I have (i.e. will it give me 2 links) or will I just have to get a longer chain?
If I can't find a relatively inexpensive 46 outer ring, would going down to 48 give me enough clearance?
How much of a difference really, would it be between 46 and 48? Is it basically negligible?
Finally, what chainrings would be good with this setup? 46t seems to be hard to find. Sugino makes one, but it lacks ramps or pins, which I've been told I should have with the 10sp setup if I were not replacing the old bipace chainrings, maybe I'd try to make it work, but if I'm replacing them anyway, I'm thinking it probably makes sense to just get chainrings designed for a 10 sp system. SRAM makes a 46t as well. I'm leaning toward the FSA pro road rings, but it comes only in 48, not 46.

Any advice would be really appreciated. Thanks.