ME6 before the patch, or ME6 after the patch? They are very different things. ME6 before the patch is approximately equivalent to an ME9 after the patch. ME6 after the patch is about halfway between an ME1 and ME2 before the patch.

The research times are detailed in the Dev Blog. Take the time in seconds from the table and multiply that by the rank of the blueprint to get the total time to research from 0 to that level. I assume if you are going to be doing ME research on high level blueprints you have Metallurgy 5. So multiply all times by 0.75. If you research in an Advanced Mobile Lab in a POS, you can multiply the times again by 0.75. A regular Mobile Laboratory will have a multiplier of 0.7. The Hyasyoda Mobile Lab will have a multiplier of 0.65. Unless explicitly mentioned, I have not counted researching in a POS in the time quotes I have given here or elsewhere, because it seems very dangerous to store capital BPOs in a POS. You also run the risk of taking it down and losing multiple months of research time.

Ranks of all blueprints can be determined by looking at the "research material time" on the blueprint, converting that to seconds, and then dividing by 6000. Orcas are rank 820. Freighters, dreads and Carriers are rank 854. Rorquals are rank 1024. Supercarriers are rank 1707. Titans are rank 3414.

You asked for freighters. So for the rank 854 blueprints here is a chart normalized by how much better than an unresearched blueprint it is:

Benefit.........ME Level and Total Research Time
0%................ME0 both pre and post Kronos. 0 Research Time
1%................ME1 post-Kronos: 18 hours, 41 minutes
2%................ME2 post-Kronos: 1 day, 20 hours
3%................ME3 post-Kronos: 4 days, 10 hours
4%................ME4 post-Kronos: 10 days, 12 hours
5%................ME1 pre-Kronos: 1 month, 14 days or ME5 post-Kronos: 24 days, 22 hours
6%................ME6 post-Kronos: 1 month, 29 days
6.67%..........ME2 pre-Kronos: 2 months, 28 days
7%................ME7 post-Kronos: 4 months, 21 days
7.50%..........ME3 pre-Kronos: 4 months, 12 days
8%................ME4 pre-Kronos: 5 months, 26 days or ME8 post-Kronos: 11 months, 5 days
8.33%..........ME5 pre-Kronos: 7 months, 10 days
8.57%..........ME6 pre-Kronos: 8 months, 24 days
8.75%..........ME7 pre-Kronos: 10 months, 8 days
8.89%..........ME8 pre-Kronos: 11 months, 22 days
9%................ME9 pre-Kronos: 1 year, 1 month, 1 day or ME9 post-Kronos: 2 years, 2 months, 8 days
9.09%..........ME10 pre-Kronos: 1 year, 2 months, 15 days
10%.............ME10 post-Kronos: 5 years, 2 months, 13 days (PERFECT)

Therefore, for a MOROS for example. Pre-Kronos it becomes effectively perfect at ME6. You could research it for 8 months 24 days in an NPC station to get it there. Post-Kronos, you need an ME9 bluprint which will take 2 years, 2 months, 8 days.

This doesn't consider that Pre-Kronos, you can research it in a high-sec POS. That will take only 6 months, 18 days. If you get war-decced, you can take the POS down and you lose at most 32 days of research. Post-Kronos, you can try to research it in a high-sec pos. It would take a total of 1 year, 6 months, 14 days to get to ME9. But then if you get war decced you either risk losing the blueprint itself or over 10 months of research time.