[c-nsp] Replacing a 2611 with PIX 515E + PIX 7.2

[Silly Questions]

Hello there,

I have three IOS routers in different sites all interconnected via
OSPF over GRE over IPSec. It's working perfectly. One of the routers
at one of the sites is getting overloaded due to the IPSec, so I want
to replace it with a PIX running 7.2 code.

The PIX doesn't support GRE so I have to re-think how this is all
setup and I'm looking for suggestions. I'm not sure if I should get
rid of GRE across the board and just do OSPF over IPSec (I'm not sure
if IOS can do straight OSPF over IPSec without a tunnel of some sort,
but it appears PIX 7.2 can) or what my options are here.

Any thoughts welcome.