Ever since purchasing the Ascent GMT I've been wondering about how it and the San Martin GMT stack up, I've done a few side by pics. So the San Martin is a 39mm and the Ascent 40mm but the 1st thing you notice is that the Ascent wears like a 39 and the San Martin like a 40. When you handle them I feel like the San Martin edges out the Ascent in almost every department, everything feels just a bit more premium but then the Ascent just comes together a bit better giving you a better overall wearing experience. All in all they're incredibly close but if you factor in that the San Martin cost about $300 less than the Ascent it takes the best bang for your buck title.
If I had to keep one and sell one, it would be tough but the Ascent would be the one I'd keep.