If you're interested in which is more "fun" a better match, competition-wise, would be the 4.6is or 4.8is. The 4.8is is a great match for the manual GTS...the 4.6is a match for the tiptronic GTS. The 4.8is (stock) is comparatively as refined but it holds a slight performance advantage over the GTS. The E70 4.8i is definitely as refined as the GTS but no match in a performance comparison but still "fun" to drive. However, i believe the E70 holds a better resale value than the GTS and is not as expensive.

This is of course my opinion based on experience as i've driven the vehicles mentioned. A good friend once owned the manual GTS but switched to the tiptronic. The GTS manual is a blast to drive but is a bit cumbersome in traffic.