Here on a core 2 duo laptop development machine, X3 shows the splash banner for about 15 seconds before showing the sonar window. Same machine, Plat shows the splash for 50 seconds and only during the last 10 to 15 seconds is there any hard drive activity.
 
After it's up, it runs nice and quick though.
 
Win 7 x64 4 gb ram
 
:Ron

Mine is quite snappy

bitman
Here on a core 2 duo laptop development machine, X3 shows the splash banner for about 15 seconds before showing the sonar window. Same machine, Plat shows the splash for 50 seconds and only during the last 10 to 15 seconds is there any hard drive activity.
 
After it's up, it runs nice and quick though.
 
Win 7 x64 4 gb ram
 
:Ron

What Audio card are you using?

On my machine, 
W7 Developer,   i7, 16gb ram
M-audio profire 2626 
 
64bit platinum starts SLOW
32 bit Platinum starts  INSTANTLY
 
no idea why.
I'm using 32 for now.

I have a Core 2 Duo 6 GB mem with a Tascam FW-1884. I don't really see much difference over X3E for start times.
It takes a while to load a fair sized project though.
Opens 4 GB project in about 60 secs (7 DIm Pros, AD1, 15 audio tracks).
Open task manager and watch the memory size during start. WHen it looks like it is doing nothing you will probably see the memory increasing to a few GB as it loads synths and samples etc, then boom... the Sonar windows open.
 
32-bit will be snappier than 64. Advantage of 64 is > 4GB memory. I could not open project above in 32. It might open but would drop out since the samples could not all be in memory and the disk would be thrashing trying to keep up.

Platinum starts faster for me.
First start, almost took a nap while waiting but after that, faster than X3e x64.

Seth Kellogg [Cakewalk]

bitman
Here on a core 2 duo laptop development machine, X3 shows the splash banner for about 15 seconds before showing the sonar window. Same machine, Plat shows the splash for 50 seconds and only during the last 10 to 15 seconds is there any hard drive activity.
 
After it's up, it runs nice and quick though.
 
Win 7 x64 4 gb ram
 
:Ron

What Audio card are you using?

Realtek HD audio (onboard) with ASIO4All
 
Sorry for the delay in response, I had to go walk the dog.
:Ron

I suggest you get an external interface. RME or Focusrite are solid.
Do the task manager memory thing. If you don't see the memory steadily increase, some driver or hardware is causing a delay.
ASIO4all is a last resort (laptop etc).

 I think 32-bit may start faster since it cannot load as much into memory as x64 and 32 loads expecting to load samples and stuff from disk later as needed.. With x64 Sonar knows to put as much stuff in memory as possible and this takes more time. Also the actual 32-bit code is somewhat smaller than 64 so this loads a little faster.
If you have I7 x86 then it is fast enough to get stuff from disk so your project still works. If you kept increasing project complexity, eventually 32-bit would choke being limited by on the fly disk access . 64-bit would have stuff in memory all the time and will handle truly massive projects.
Try the task manager memory size thing. Sonar should not be idle for any length of time on start. IT should pretty much be loading stuff into memory all the time until the Sonar windows appear. 

X3e was even quite long on start up - the first time around i.e. after windows just loads
after it's been open once, then it's pretty snappy. May be plat is the same in that regard..?