RAM upgrade for Studio 1749

Hi,

I have a 2010 Studio 1749.  It came with 4GB RAM (2 x 2GB PC3-8500S).  I'm thinking this equates to 1033MHz?

I'm almost constantly operating at 90%+ RAM capacity so hoping an upgrade to 8GB (max for Win7 Pro I believe) will help a bit.

Having dug about for an idea of what I can install I have found two conflicting pieces of advice, both from Dell people on the forum I believe. 

One says Studio 1749 can only run with 1066 and 1033 MHz speeds RAM

http://en.community.dell.com/support-forums/laptop/f/3518/t/19529847

and one says the system supports DDR3 1066/1333 MHz SODIMMs

http://en.community.dell.com/support-forums/laptop/f/3518/t/19640823

Googled 1749 RAM and this result comes up regularly. 

www.offtek.co.uk/.../899687

This is 1333MHz I think?  Due to the conflicting info mentioned above can anyone advise if this is compatible with my Dell Studio 1749 (i5 M540).  I'm thinking so.   And can anyone also advise is this is about the best I can put in spec wise?

thanks

Jon