Upgrading Fully Buffered RAM

[MPapendrecht]

Hi!

I got a Dell t7400 workstation (source1) for my birthday, hurray!

I want to upgrade my RAM to 8 or 16 GB, but from the internet it seems I can choose about almost nothing.

On servermonkey I found these modules to be compatible with my system (source2).

I opened the case and I found these numbers on the sticker:

   hynix 1GB 1Rx8 PC2-6400F 555-11

And on the slot itself: Lotus 1.8V.

 

My Questions:

1. Why is the current RAM speed different compared to the recommended speed, and why does it work (it looks like it isnt compatible)?

2. What are my options for upgrading my RAM? 

 

Some usefull info: I live in the Netherlands, thus servermonkey gives me 90 euros shipping fee, which makes this RAM very expensive. I found some in Germany, but I wanted to ask if it is even the best option before buying anything. 

 

I hope anyone can help me deciding on this one,

Thank you in advance,

MPapendrecht

 

Source1: http://www.dell.com/downloads/global/products/precn/en/precn_t7400_specsheet.pdf

Source2: http://www.servermonkey.com/parts-and-upgrades/memory/dell/precision-t7400-memory.html