Importance of arm length?

Hi! I have just purchased a VPI HW-19 mk III online (won't arrive until next week). The plinth is cut for the VPI standard budget arm, Audioquest PT6. I don't own an AQ PT6, but I do own a Sumiko Premier MMT. The MMT is a slightly longer arm. Effective length of 239 mm for the MMT vs. 229 mm for the AQ. The mounting distance for the MMT is 221.7mm, for the AQ it is 211mm. A few questions maybe someone could answer for me...1. Is the difference in length significant enough to make a difference, or can I use the Sumiko in the AQ cut plinth? 2. How does the Sumiko compare with the AQ? I have an opportunity to purchase an AQ PT6 at a good price, and wonder what the tradeoffs would be if I went with that arm vs the Sumiko? If I stick with the Sumiko, would I have to get a new plinth and have that cut for that arm and would it be worth it? Thanks much, Ben