win2008 r2 - terminalserver slow during daily business in office and sql bases client software

Hello, 

System: 

1. windows 2008 r2 - 30 GB RAM - RAID 50 - hp ml370 g6 - 8 x 300k sas drives
2. sql 2008 std. with approx. 10 GB Database
3. approx. 15 User, 5 x Poweruser
4. word, outlook, sql-based erp client called isy,  firefox, java base client, ESET NOD are the daily running software
5. main RAM usage goes to SQL Database with 5 GB, then the isy clients with each 100 MB

Problem: the main software is the sql-based erp client called isy - he showed me that e.g. opening pages in the programm takes  e.g. 10 seconds. this action is done daily many times and it is required to improve it.

My ideas:

1. the whole server has wrong Raid 50 for SQL Database
2. battery backed write cache is installed as far as I know
3. comparing night / daily speed not done yet - but speed problems are reported to by random
4. windows shadow copy only needs a couple of minutes
5. backup is running fast at night
6. RAM was initially by 18 GB and since new software installation 2 month ago customer claim increased and RAM usage was about 99% at day.
7. RAM was recently increased to 30 GB with  effect that RAM Usage is now about 70-85% at day
8. do you think RAM increase to 64 GB would make a different?
9. "Isy" Software Provider wasnt involved in the problem yet
10. I think I will try convert the power users to local workstations with SSD Drives

thank you for your thoughts