I don't believe there are memory upgrades available for the SUP4 for the 4507. You cannot combine the supervisors for more processing power. The secondary supervisor is strictly for processor redundancy within the chassis.
With the 4507 chassis you can use the SUP5 which will give you slightly more throughput over the SUP4 and that's about it. The SUP6-E will give quite a bit more performance and many other features. Depending on your projected growth you might consider purchasing a 6500 series switch. Here's the data sheet for the supervisors.
Something to keep in mind, size the supervisor to the bandwidth it needs to support. With just five line card slots available in your 4507R, and each limited to 6 GBs to the fabric (non -E chassis), there's no benefit using a "faster" supervisor unless you have 10 gig uplinks, move to the 4510R, or move to the -E chassis. In other words, the Sup-IV, should run your 4507R at wire rate, for what the chassis and uplinks support.
If you need more ports, slots, or more bandwidth to the line cards, then you'll need to re-evaluate the whole hardware combination.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...