I have an ADCMT 8252 which I could see being quite similar to the 5350 but also have a 200V voltage source for resistance measurement. I have not tested it out to much in detail but it is doing a very good job where 3458a is struggling, like low current, high resistance and need for very low current load voltage measurement.
I also have a ADMCT 5450 ultra high resistance meter. That is also very good, but lack the voltage functionality and seems to have a slight edge for low current measurement. It is on my todolist to compare these and my Keithley 2450 in low current measurements.