Simulate an older machine respecting its overall capabilities?

Question

Note I recon my question's main goal isn't programming-related; its means though are best known to programmers (for a reason ;)) That said, feel free to advise some other place should you believe it'll be viewed by better informed people in this complex field.

We're getting close to deploy refurbished PCs with carefully optimized systems at the local #diy facility I'm volunteering in. It's « The devil is in the details » time.

Question 1: What would be your specs sheet to simulating older machines keeping reasonably close to their overall capabilities?

Goal

Help testing OSes and apps capabilities on a few end-user IRL scenarios: kids/guests/digital-iliterate-person as well as retro-gaming/experiment-and-discover scenarios. And then configure/optimize the chosen setups.

Means we oughta garanty --and therefore test-- the box with optimized system duo capabilities for ( browse the today Web -- html5 incl. Plays videos View photos Edit office documents ), that's it!

Target

Circa 2000-2005 boxes: mostly SSE (3DNow!) CPUs such as Ahtlons (k7, 32-bit) and Pentium (P6), 7200 IDE hdds, FSB 400/DDR400 (or below) SDRAM, and "some kind of" AGP graphics.

Means

1. Specs sheet, atm it looks at the target's:

   • cpu instructions *
   • cpu frequency *
   • FSB/bus speed and bandwidth
   • IO speed and bandwidth *
   • graphics *

   * is possibly addressed in my current set-up (i.e. "well enough").

2. Current old box emulation set-up

   • Core i3 @3.3ghz with DDR3 1600 running Arch linux [1]

   • virtualization set up

     cpulimit -l 60 \ qemu-system-i386 -cpu pentium3,enforce -enable-kvm \ -m 1G -vga std -display gtk -enable-kvm -hda hdd.img

   First, it tries to stay below-or-equal the target CPu frequency; b) to its instructions set:

   /proc/cpuinfo (and google chrome ;) )

   ~$ test@guest inxi -f 
   CPU:   Single core Pentium III (Katmai) (-UP-) cache: 2048 KB clocked at 3292.518 MHz     
          CPU Flags: apic cmov cx8 de fpu fxsr hypervisor mca mce mmx msr mtrr pae pge pse pse36
          sep sse tsc vme x2apic
   

   c) to the available RAM, d) hdd.img stands on a spinning 7200 Sata HDD and has qcow2 format to try sticking closer to the target IO specs. e) to the older 2D rendering capabilities AFAIK Qemu/KVM -vga std great gpu emulation ;) makes it a good choice to simulate that

Question two: Are the following limits really impacting?

• It's unclear whether Qemu KVM succeeds to restrict the vcpu to the chosen cpu model e.g. shouldn't -cpu pentium3 show a 250 KB cache?
• IO subsystem (big point here especially for finding out the correct Linux kernel virtual memory settings). It'd be really cool to stick to less-or-equal an IDE bus and 20 GB HDD efficiency.
• What about the FSB bus/memory subsystem part??

Alyernatively, do uou know of tool, tips or tricks to achieve a better "reasonably equal-or-less" to the target capabilities VM set-up?

[1] limited time opening at the diy facility make it necessary to fine tune at my place. Host has VT-x set but no VT-d capabilities.

EDIT: How can I simulate a slow machine in a VM? and Slow down CPU to simulate slower computers in browser testing, cover the cpu speed part. How To Simulate Lower CPU Processor Machines For Browser Testing and Emulate old PC? [closed] too and are centered on Windows host.