Mounting CDs has always worked so far, just add -ide 2m to the IMGMOUNT command to attach the CD-ROM to the secondary master IDE port and it should work. I think it hasn't "worked" yet for some people because there are possible mistakes in IDE auto-assignment that need to be worked out.
(I personally would love to see a DOSBox provide a QEMU-style console to permit inserting and removing CD and floppy images while booted into an OS or running a DOS game BTW).
It seems like Windows 32-bit paging in general kills the dynamic core's performance, and once the dynamic core is struggling, things in Win98 crash a lot. The IDE driver seems to "help" Win98 in that way, perhaps Win98 figures it can page out more of the DOS region when IDE is used? For example, when IDE is in use by Win98, the instance the "Enter Network Password" dialog appears, the dynamic core slows to a crawl, and after that when bringing up the desktop, that's when EXPLORER.EXE begins to crash at times from within KERNEL32.DLL at <module> 0000:xxxxxxxxx for some reason. I'm wondering if the KMixer thing with Sound Blaster 16 audio also kills the dynamic core in the same way.
UPDATE: The strange thing is I see the same slowdown in Win95 OSR2, except that OSR2 doesn't crash.
UPDATE: Windows 95 SP1 generally doesn't slow down, but if you run a 32-bit program like the Microsoft Exchange program, then it triggers the massive slowdown in the dynamic core.... or not. I can't seem to reproduce it now. Win95 SP1 is generally quite fast but at random, sooner or later, the dynamic core isn't able to run full speed anymore.
UPDATE: Win98 setup runs smoothly until it too causes the massive slowdown in the core, then things start to crash.
DOSBox-X project: more emulation better accuracy.
DOSLIB and DOSLIB2: Learn how to tinker and hack hardware and software from DOS.