What would be a good upgrade from Cisco 6506-E?

The 6807 is the natural replacement for this.

4K isn't a replacement for the 6K.

You are right Craig.  I meant to tag ur comment as the solution. But I was doing this on my phone and this happened.  I'm new to EE.  Anyway I can change that?

Thanks again for the recommendation!

A 4K might be able to replace a 6K at the core. It did for me. A 3K also might be okay, but is limited it's ability to support storage networking. Without knowing anything about what the needs of the network are, we can't make any recommendations regarding what is actually appropriate for the environment.

How, kevin? There are linecards in the 6K that you can't put in a 4K chassis. The 4500-E isn't a core switch and the 4500-X isn't capable of taking linecards. The 6807 is the replacement for what's there already.

There are many possible network designs, with various types of equipment that can be procured. OP is also asking about replacing 6506 with a 3850, which also isn't a core switch, and doesn't take line cards. Without a better description of the environment or the goals, it's hard to make any recommendations. It seems that cost may or not not be an issue.

a 10G line card could be installed in the existing chassis. A 4500-X could be added to the network for the 10G connectivity. It could even be made into the "core", and the 6506E could be made into an access switch.

I hear you, but the question asked for a good upgrade and mentions linecards. For that reason alone a 3850 and 4500-X are non-starters.

The 4500-E isn't a core switch; never has been and never will be. That leaves the 6807 which Cisco clearly state is the new 6500.

FWIW the 3850 10G mGig switch will likely replace the 4500-X in the future.

Is it worth to upgrade the chassis at all or replace line cards with 10Gb SFP?   The cost of the 10Gb line cards is expensive.

Totally depends on when the end goals are. Is the goal just to get some 10G? Does that 10G need to be low latency to handle microbursts from storage?

The 3850 looks like it's designed to be an access switch in wiring closets. That's fine, but it isn't a large buffer/low latency switch like a 4500-X for top of rack east-west datacenter applications.

Maybe the Nexus line is a good fit as originally proposed, but Matt needs to give more information.

The 3850 looks like it's designed to be an access switch in wiring closets. That's fine, but it isn't a large buffer/low latency switch like a 4500-X for top of rack east-west datacenter applications.

So you're just confirming that the 3850 isn't a replacement for a 6500.

As I said, you'll see soon enough that the 3850 will be the replacement for the 4500-X, so that blows the 4K out of the list too.  The only option therefore is the 6807, as I've already said.

If you're replacing a modular switch with a non-modular switch that has 25% the port density of the original switch, it's not an upgrade IMO.

I don't think "it depends on what you want it for" really comes into it.  The question is "What would be a good upgrade from Cisco 6506-E?".  The vendor says the replacement for the 6500 is the 6807, so that is a good replacement.