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Yes, a longer top tube means a greater distance from your saddle to the handlebars. On road racing frames, manufacturers seem to spec slacker seat tube and steeper head tube angles to give taller riders enough space to fit into, whilst maintaining a short wheelbase.
If you currently have an "aggressive" fit (i.e. lots of saddle to bar drop) and you want to maintain that, then you'll probably need an inline seatpost with the slacker seat tube, otherwise your hip angle might be a bit tight and you'll struggle to spin smoothly.
But, if you want something a bit more "relaxing" go with the slacker seat tube and raise the bars up a bit.
macaroon-
Cheers for the explanation. Turns out I got it wrong, both ST are the same in the 56 size, but a difference of 1 degree in HT which I guess accounts for the shorter reach, slightly offset by a longer wheelbase.
Basically there's too many factors at play for me to fully analyse what the difference would be, but the answer is probably fuck all.
Polygon
Anyone care to explain the (probably pretty basic) principle of ETT vs frame reach? Trying to get my head around how more ETT but the same reach could possibly equate to about the same fit. About 1.5 degrees difference between the two seat angles, so I get where it comes from, but what difference would it mean in terms of fit? Surely more top tube = more stretch, even if the reach is about the same?
Oh, and I'll go with the usual tactic of recommending the only thing I know and say BW for Bristol bike fitting.