-RC1 more stable when compared to -STABLE

Recently I was running a number of tests against 5.3-STABLE (btw, 
RELENG_5 labeling the system as 5.3-STABLE might be very confusing in a 
situation where there's not even a 5.3-RELEASE yet, if one doesnt follow 
how -STABLE are treated compared to "security branchs"), in a SMP system 
with multiple SATA RAID, and it was not responding well, had a number of 
freezes under stress tests; Some of those problems could be minimized 
running BSD as the scheduller instead of ULE;

Now -RC1 shows the same performance 5.2.1 used to, also w/ SCHED_BSD, 
but with ULE it stops responding well sometimes.

This first system is a dual-P4 3.0; but with older SMP systems I get a 
problem on 5.3 that does not happens on 5.2.1;

The system is a 4-proc Pentium Pro, it installs fine, but when we start 
using more CPU (say, running stress(8) or building a port) it panics w/

Panic: APIC: Previous IPI is stuck
     cpuid: 0
     boot() called on cpu#0
     Uptime: 3h44m23s
     Cannot dump. No dump device defined
     Automatic reboot in 15 second - press a key ...
     cpu_reset called on cpu#0
     cpu_reset: stopping other CPUs
     Panic: APIC: Previous IPI is stuck
     cpuid=0
     boot() called on cpu#0

Under 5.2.1 it runs fine.

What kind of more detailed info can I send to help tracking this behaviour?

-- 
Atenciosamente,

Patrick Tracanelli