I'll give my two cents, as someone who has been building furniture for a living?for 20 years. First of all, I'd never spend $10K on a new saw. There are so many used sliders on the market since cabinet shops no longer really want them around. You can pick up Altendorf and SCMI sliders for significantly less money than that. I bought my Panhans, 10'+ stroke for $2500 including probably $1000 worth of blades. The thing is basically bomb proof. Just made my first repair on it in a dozen years, a $30 switch for the scoring motor. You have to be careful what you buy, you don't want something that was abused by a bunch of employees. If you are sold on Felder, they come up used often as well. If you're going to spend close to 10K, you can probably get a late model K700, or KF on the used market. One good thing is they usually come out of hobby shops or small pro shops with an employee or two. We have 2 KF700's in our coop shop, both with the 80" stroke. I'd never have a slider that short as my only saw, unless you only build furniture out of solid wood and rarely handle sheet goods.

Plan on bringing in 3 phase if it's an option, or going the phase converter route. I personally would not buy a Felder with a built in VFD. Both of our machines have had issues. They are 2001 vintage. Part acquisition was a nightmare too. I'm talking a month plus of down time. Having the ability to run any 3 phase machine opens lots of possibilities. Single phase machines always fetch too much money on the used market since the market is so much bigger.

I have not personally used or seen a K500, or the other saw you mentioned so I cannot speak to them. Don't be afraid to look at used. Sliders are simple machines (or can be). My Panhans was built mid 80's and performs like a champ every single day. I was straight line ripping 11' long 8/4 white oak on it over the weekend. I just had to remove one clamp to get the full length. A thing of beauty.

Jason