"only slightly faster" is correct and usable in written English.
You can use it to describe something that is a relatively small advantage over something else. For example: "My new laptop is only slightly faster than my old one, but it was worth the upgrade."
Thereafter, they would grow only slightly faster than inflation.
Pay for most families has risen only slightly faster than inflation.
When they flew backward, they beat their wings only slightly faster, at 43.8 hertz.
That was only slightly faster than the meagre 0.1% growth in the second quarter (0.3% annualised).
In fact, the national median price rose only slightly faster than inflation from 1950 to the mid-1990s.
But for all of 2000 the core index grew just 1.2percentt, only slightly faster than in 1999 and about half its pace in 1998.
So the Chrysler plan announced today will produce only a slightly faster shrinkage of its manufacturing work force than one of Chrysler's main competitors is already achieving.
While there have been some changes in the DSP income disregard, tax rates, and in its nominal benefit guarantee, over the entire period from 1970 to 2011, the break-even income threshold where DSP benefits go to zero has only increased slightly faster than average wage earnings.
A fed-batch experiment, in which the same total amount of solid was added but in equal aliquots at hourly intervals, was also trialled in this study but did not show any major advantage over batch addition as there was no increase in the final hydrolysis conversion, only a slightly faster initial liquefaction rate.
Overall, mean blood glucose levels differed only slightly between fasting and non-fasting individuals: 5.1 ± 0.8 mmol/L in fasting men, 5.2 ± 1.2 mmol/L in non-fasting men; resp.
Comparing the new estimates with earlier estimates based on overlooked cancers found in Spratt and colleagues [ 9] we found generally good concordance, with only slightly more very fast-growing tumors (Table 2).
