bluescsi is probably you cheapest and easiest to build option, its code base is regularly updated, pretty sure CD-ROM iso support is available now. however
@cheesestraws bring up a real issue, overdriving a. cpu to get better performance probably isn't a good idea in terms of reliability and such. while its probably fne, its seriously a bad practice for production devices of any kind particularly when data is concerned. overall R/W performance isn't to bad for a vintage Mac
ZuluSCSI and SCSI2SD are bother great options if you have the money, both should perform the best at R/W though someone should confirm that in case in remembering wrong.
RaSCSI is another option that uses a raspberry pi, but has added features available like networking. I haven't used one myself but Its on my 'to buy and mess around with' list. it does take a few seconds to boot though so depending on you setup that could be a deal breaker or not. again the R/W is meant to be good too. a raSCSI is probably more practical for those needing network support atm, but if you check the wiki there's lots of potential things that can be done with it beyond just a scsi hdd emulator.
the last option would be the Scuznet by
@saybur , it also has networking built in and initial CD-ROM support is there too. I run one on my Mac se/30 daily drive and get around 1.5mb Read and 1.3mb Write performance. however the firmware still has a few minor issues in some use cases in respect to performance as well as some future features still to be added. last time I spoke to Saybur he said he plans to work on the firmware more when he has some time. so while it works fine for me, this also may or may not be a deal breaker.
another option too depending on what Mac model you have would be to use a CF to IDE adaptor