Yeah I was wondering about that....what's the advantage, more spin? Federer plays with the gut mains/ poly crosses....if 80% of the feel is in the mains.....can you please elaorate the tradeoffs, thanks.
I'm not Tom, but My suggestion would be to ask yourself carefully what you are trying to achieve before sinking ~20$ into bare string costs. I find that both set ups have their merits...
The Poly main is obviously going to be more durable, and the gut cross will help soften the string bed up a bit. This may be something you don't really want with the energy mains. (It may get springy). IMO, if you really need the durability, this is about the best you can do with a cross. It's more arm friendly than a syn gut (although this isn't a HUGE difference), and it'll hold it's tension longer.
The Gut main/poly cross is kind of a new "phenomenon" in the string world, as far as i'm concerned. It gives the overall "feel"/response of gut, but the poly cross sucks a little bit of the resilience (resulting in less power) out of the job, which is right up many players' alleys. If you don't want to risk the cost of a set of gut, you can try both set ups with a nicer multi (NRG2, NXT, etc) and determine which style of set up you prefer.
I think in either case you are forfeiting some aspect/partial benefits of the main string. Namely, the ultimate control/very very low power of poly, or the liveliness and very very good comfort of the gut. I have found merits (as i mentioned) in both styles of set up, but you might want to ask yourself what you are looking to get from the set up. I think if you aren't needing the high durability of the poly, you might try the gut set up. It "deadens" the job a little bit, but you still retain excellent feel and pretty good touch.