What is your weight, and what size and type sails are you using?
Narrower tails normally do not give earlier planing, and lighter also does not necessarily give earlier planing.
Better technique, lighter weight sailors, larger rigs and larger span fins are normally the way to earlier planing.
What fin are you using on your GO 170 currently?
Is yours a 2005 GO 170 with a Drake Race 560 (56 cm) fin?
2005 GO 170 Specs:
170 liters; 256 cm long; 90 cm wide; 62.2 cm 1' off tail width; 10.9 Kg's/ 24.03 lbs. weight; Deep Tuttle fin box; Drake Race 560 (56 cm) fin.
Here's a link to the 2005 Products archive:
A Carve 162 in Technora weighs 9.3 Kg./20.5 lbs. (3.53 lbs. < than your GO 170 ) and the Wood Construction Carve 162 weighs 8.9 Kg./19.6 lbs.(4.43 lbs. < than your GO 170).
I don't think a 4.43 lb difference is going to result in any thing like "earlier planing, but if you want a more "lively" board a Carve might be a very good choice. If you weigh under 200 lbs. (90.7 Kg) and have some large > 9.0 m2 rigs I think the Carve 144 or 133 would be a better choice if you plan to keep your GO 170. If not, then the Carve 162 would be the right choice, but you will lose some low wind range vs your GO 170 due to the narrower overall and narrower 1'off the tail widths.
Hope this helps,