IDK if this helps you any but, I have a stock 2159 and I run an 18" 3/8 0.050 full comp setup and it handles it quite well. I have a 20" bar but have never tried it on the 2159. I imagine it would be ok with it but might slow a little with the tip burried (20" is max recommended per OEM). It would be interested in seeing the 2159 after porting...
OTOH, a 2260 is meant to be the more full time professional saw over the 2159 and 2258 and toutes about one half more HP more power (advertised). If all three saws were available for the same price I would go with the 2260, more power, same weight and less vibration over the 2159.
I'd probably pass on the smaller 2253. Eventhough its over a LB lighter than the 2260, it also has almost 1 hp less power. The difference is 50 vs 60 cc's. You'll want those extra cc's when you put that 20" bar on IMO.