I was in the exact same situation as you about a year ago. I had a KT7A and I wanted to get rid of it, and I had SDRAM and did not want to buy DDR-SDRAM.
Yes, the ECS K7S5A is your only choice if you wish to stay away from VIA. That's what I have right now and it works very fine with me. It's faster than the KT7A (the ATA controller rocks!) and it's far more stable. However, I must warn you that the K7S5A is a very fragile motherboard. Check if you have the following:
1. Very, very, very good ram. I have Kingston and had no problems with it. However, forget about generic or even mid-range DIMMs. Many DIMMs were rejected by my K7S5A.
2. A very good power supply. I have an Enermax 350W and works fine. Many people have reported problems due to no-name power supplies.
Also, be aware that this is not an enthusiast board. That means no overclocking. The layout of the board is horrible, so your airflow setup might be hampered. Also, I’ve heard that the K7S5A only takes Athlon XP's. However, mine takes a thunderbird 1333 just fine.
So, I do recommend that board if you don't mind having small to very major problems. It’s an adventurous path. I wanted to experiment with this board and it turned to be much better than I thought. However, I had the right components to support it. Keep you KT7A even after a few months of using the K7S5A. It may come handy :wink: .
Also, please note that although the KT133A is not a very good chipset, the KT7A experienced problems of its own. Problems not present on other KT133A boards. Like Frank said, it you told us what problems you were experiencing, maybe we can help you solve them. Also, there are other KT133A boards out there. Maybe just changing brands will solve the problem...You'd be surprised how Abit boards are so poorly designed.
Finally, take a look at this thread about the K7S5A :