I've never skated any Indys besides standard. I fear change .. But tell me more!
Indy makes two versions of the 55mm high truck: The standard Indy, and a hollow axle version. Both of these have the standard Indy base plate, which as someone already mentioned, can have the hardware holes oval-out with time.
Indy also makes two versions of the 53mm* high truck. The forged hollow (hollow axle and kingpin), and the titanium (only the axle is titanium). These have the forged base plate, which is stronger and thinner than the standard Indy base plate. Thus, the base plate holes won't oval-out, and the truck is lower than standard Indys. Prior to the release of Stage VI Indys, all their trucks were 53mm high. When Stage VI came out, they made the standard version 55mm high. This caused a lot of controversy. Some like the added height. Others hate it.
I have ridden both the 53mm and the 55mm version. I notice a difference. First, with the 55mm version, the board hits a higher angle on nollie/ollies. This gives you a better "pop" (see this video where Paul Schmitt talks about the physics of board height/angle and pop.)
).
I definitely notice this. However, it can also lead to more "ghost popping" at times (when tail never actually hits the ground). The 55mm also seems to turn a bit better, because there is a bit more wheel clearance. Last, the 55mm can feel a little "tipsy because of their height. I notice this
the most when doing 50/50s on round rails.
The 53mm don't seem to pop quite as good, but have less ghost pop, and feel more stable because they are lower to the ground. IMHO, 53mm is a great height that is halfway between a lower truck (Thunder) and higher ones (standard Indy, Ace, etc.). Although it isn't that much, you
can notice a weight difference between the forged hollow trucks, and the standard Indy.
If you want the lightest Indy, with height options, get the titanium version (comes with lower forged base plate), and just add a thin riser if you want that 55mm height. You can
always make a 53mm forged Indy perform like the taller standard 55mm Indy (e.g. w/1.5-2mm riser), but you can
never make a 55mm standard Indy perform like the 53mm forged version.
*Indy claims the height on these is 53.5mm. Every time I've measured them they were 53mm.