With the GGTS you get a lot of choices for battery configurations.
If I were stepping up from 3.7v, I would try 6.0v (2 rcr123 3.0v) on an i7 or an i6 atty. The 6.0v on an i7 feels a bit more like 5v volts to me. I'm not sure if this is true to the math or what the resistance in the attys are..just based on experiences.
Rob has the yellow Tenergies I think, I like those batteries better than the blue ones with a higher mAh rating
http://www.vaporkings.com/Tenergy_RCR123A_3_0v_LiFePo4_batteries_p/battery-rcr123a-3.0v-lifepo4.htm. They always seemed more reliable to me, and I didn't see a huge difference with battery life.
The downside of this, is you can't get the 3.7v experience with just one battery. But honestly, one of the larger 18650's
http://www.vaporkings.com/AW_Orange_18650_3_7v_1600_mAh_LiMN_battery_p/battery-18650-orange.htm will let you vape all day long and then some on that one battery. Assuming you also want to occasionally vape at 3.7.
So *my* opinion is... 2 of the yellow tenergy 3.0v batteries for 6.0v and get yourself an 18650 for 3.7... that also gives you the option of using LR atties as well. Get either i6 or i7 atties, I think both will supply you with more throat hit than you are used to with your lower voltage 510.
As far as nic goes...You will get harder TH with HV..so be prepared for a lot more oomph from your vaping. If you have some of your 24mg juice, you should try that first, you can always go lower later... but if you get something too low, you won't be satisfied, and you may suck through a ton of juice....especially with the AFS.
GG users have also been having a WHOLE LOTTA FUN with cartomizers in the GG AFS too, check out the GG subforum
http://www.e-cigarette-forum.com/forum/gg/, and ask questions there as well.
Thats just my two pennies.... really though, you will have to experiment... and find your sweet spot... but thats half the fun
