Well hosting aside here is a comparison between Ideal_Comfort and Adapt
Ideal Comfort (stock X-cart 4.5.2 with just a few extras taken from
http://trainingpen.com/manufacturers_carousel/) :
Total HTTP Requests: 217 Total Size: 1245430 bytes
Adapt (taken from
http://demos.xcartmods.co.uk/adapt/):
Total HTTP Requests:228 Total Size:2760716 bytes
Now admittedly this is not just the difference in skin. The site would need to be identical in every other way to achieve a true comparison. Images play a large role, and the adapt template has the slider on the home page.
But initially it appears to me that adapt is not very "lite". It is a robust template with lots of extra features, so you can expect it to weigh a little more. For me the extra weight is pretty bad, I usually try to optimize X-cart to come in at around 120-130 requests and about 360-450kb after compression. (BTW neither of these sites are using compression)